1. Field of the Invention
The present invention relates to a polishing method using a ceria slurry, and more particularly, to a polishing method which is preferable in a planarization process employing chemical-and-mechanical polishing (CMP), such as a semiconductor device process or an interconnection-integrated liquid-crystal process.
2. Description of the Related Art
A technique for planarizing the surface of a semiconductor substrate during manufacturing processes is one means for responding to an increase in packing density of and miniaturization of a semiconductor device. By way of an example of a polishing apparatus employed by a related-art CMP technique, a polishing apparatus described in Japanese Patent Application Laid-Open No. 294861/1996 will now be described by reference to FIG. 1 and FIG. 2.
Here, FIG. 1 is a perspective view showing a polishing apparatus, and FIG. 2 is a top view of the apparatus. A polishing cloth 115 for polishing a surface to be polished is affixed to a turntable 113 which rotates within a horizontal plane. A wafer-holding disk 114 is placed in an elevated position over the turntable 113 for holding a wafer 116 such that a surface of a semiconductor substrate, which surface is to be polished (hereinafter called a xe2x80x9ctarget surfacexe2x80x9d), is placed opposite the surface of the polishing cloth 115. The rotation center C of the wafer-holding disk 114 is offset from the rotation center D of the turntable 113 by a given distance E.
A grinding fluid supply pipe 117 for supplying a grinding fluid to a polishing surface 115a of the polishing cloth 115 and a dressing fluid supply pipe 120 for supplying dressing fluid to the polishing surface 115a are situated at elevated positions over the turntable 113. Further situated over the turntable 113 is a fluid discharge mechanism 123 for discharging grinding waste fluid produced and dressing fluid after polishing operation.
The diameter of the wafer-holding disk 114 is shorter than the radius of the turntable 113. The turntable 113 rotates in the direction designated by arrow A, and the wafer-holding disk 114 rotates in the direction designated by arrow B. A circle F designated by two-dot chain lines shown in FIG. 2 shows a locus which is drawn in the vicinity of the rotation center of the polishing cloth 115 by the outer edge of the wafer 116 held by the wafer-holding disk 114.
Grinding fluid is supplied from the grinding fluid supply pipe 117 to the polishing surface 115a of the polishing cloth 115 affixed to the turntable 113, which plate is rotating at a given speed. Simultaneously, water serving as dressing fluid is supplied from the dressing fluid supply pipe 120 to the polishing surface 115a. 
The wafer-holding disk 114 having the wafer 116 fixed thereon is lowered while being rotated at a certain speed. As a result, a target surface of the wafer 116 is pressed against the polishing surface 115a, thereby polishing the target surface. The fluid discharge mechanism 123 collects the grinding waste fluid and dressing fluid produced after polishing operation. In the manner as mentioned above, the wafer 116 is polished.
Silica-based slurry (SiO2-based slurry) has frequently been used as a polishing agent for polishing an oxide film. Silica-based slurry is characterized by uniform particle size and being unlikely to cause scratches. However, silica-based slurry has a low polishing rate. Hence, in a case where a large amount of grinding is required, silica-based slurry poses a problem. For this reason, ceria slurry (CeO2-based slurry) yielding a high polishing rate has recently come to attention and has come to be employed frequently.
Even when polishing fluid of either type is used, abrasion of recesses proceeds when pattern steps are subjected to planarization. Hence, difficult is encountered in reducing steps to a certain height or less. Further, there arises another problem of a large amount of abrasion being required until steps are reduced to the certain height. Ceria slurry with additives (hereinafter called xe2x80x9chighly selective ceria slurryxe2x80x9d) has been developed for solving the foregoing problems.
So long as the highly selective ceria slurry is employed, a rate at which recesses are to be polished is suppressed, and the smoothness of the wafer can be improved greatly as compared with the case of use of related-art slurry. FIG. 3 shows an example result of polishing operation using highly selective ceria slurry. Polishing requirements are optimized in connection with the evenness of a film remaining within a wafer surface after polishing operation as well as in connection with a range in which abrasion of recesses does not proceed, the range characterizing the highly selective ceria slurry.
In FIG. 3, the horizontal axis represents polishing time, and the vertical axis represents the thickness of a residual film. A graph having plot points xe2x80x9cxxe2x80x9d shows the polishing status of recesses, and a graph having plot points xe2x80x9c+xe2x80x9d shows the polishing status of protuberances. As shown in FIG. 3, primarily protuberances are polished until 480 seconds have passed after the start of abrasion, and planarization is completed when the thickness of remaining recesses becomes substantially equal to that of remaining protuberances. After planarization has been completed, recesses and protuberances are polished until the residual film attains to a predetermined thickness.
It has been ascertained that ceria slurry usually has a low polishing rate until 120 seconds have passed after the start of abrasion; polishing rate is particularly low within a range of 60 seconds after the start of abrasion (not shown in FIG. 3). Therefore, as can be seen from FIG. 3, the following drawbacks are encountered even when the highly selective ceria slurry is employed.
(1) In an early stage of polishing operation, there is a range in which a polishing rate is considerably slow.
(2) A polishing rate attained while planarization is under way is lower than that attained in a case where related-art ceria slurry is employed.
(3) A considerably low polishing rate is attained after planarization has been completed, and planarization of a remaining film to a predetermined thickness involves consumption of much time.
As mentioned above, highly-selective ceria slurry possesses high smoothness but yields low productivity.
A conceivable method of solving the above-described problem is a polishing process using a plurality of types of slurry. However, such a method involves an increase in the number of ancillary facilities (such as a slurry supply unit or the like), as well as a necessity of a cleaning step at the time of switching of slurry for preventing coexistence of a plurality of types of slurry. Hence, achieving an improvement in total productivity is difficult.
The present invention has been conceived to solve the foregoing drawbacks and is aimed at providing a polishing method which enables simultaneous realization of good smoothness and productivity through use of ceria slurry. There is also provided a method of manufacturing a semiconductor device using such a polishing method.
According to one aspect of the present invention, in a polishing method using ceria slurry, in which ceria slurry is supplied to a polishing surface in rotation, and a surface of a semiconductor substrate opposing the polishing surface is pressed against the polishing surface, thereby polishing the surface to be polished, the polishing processing is divided into a plurality of phases, and polishing is effected while polishing requirements are changed from phase to phase.
According to other aspect of the present invention, in a polishing method using ceria slurry, in which ceria slurry is supplied to a polishing surface in rotation, and a surface of a semiconductor substrate opposing the polishing surface is pressed against the polishing surface, thereby polishing the surface to be polished, the polishing process is divided into a plurality of phases, that is, an early polishing phase, a planarization phase, and a post-planarization phase, and polishing is effected while polishing requirements are changed from phase to phase.
According to other aspect of the present invention, in a polishing method using ceria slurry, in which ceria slurry is supplied to a polishing surface in rotation, and a surface of a semiconductor substrate opposing the polishing surface is pressed against the polishing surface, thereby polishing the surface to be polished, in an early polishing phase, polishing is effected by application of pressure greater than a predetermined pressure for pressing the surface to be polished against the polishing surface.
According to other aspect of the present invention, in a polishing method using ceria slurry, in which ceria slurry is supplied to a polishing surface in rotation, and a surface of a semiconductor substrate opposing the polishing surface is pressed against the polishing surface, thereby polishing the surface to be polished, in the planarization process, polishing is effected while the polishing surface and the surface to be polished are rotated at a speed higher than a predetermined speed.
According to other aspect of the present invention, in a polishing method using ceria slurry, in which ceria slurry is supplied to a polishing surface in rotation, and a surface of a semiconductor substrate opposing the polishing surface is pressed against the polishing surface, thereby polishing the surface to be polished, in the post-planarization phase, polishing is effected by means of applying pressure greater than a predetermined pressure for pressing the surface to be polished against the polishing surface.
Other and further objects, features and advantages of the invention will appear more fully from the following description.